This invention relates to video cameras for use in conjunction with endoscopes in medical and surgical applications. In particular, the invention relates to video cameras which are or may be attached to the end of the endoscope operated by medical personnel where an image from a selected area inside a patient's body cavity is produced external to the endoscope.
Endoscopes have established a wide variety of utility in the medical and surgical fields for viewing inside the human body. For example, endoscopes are useful in the surgical specialties of arthroscopy, bronchoscopy, colonoscopy, cystoscopy, gastroscopy, laparoscopy, laryngoscopy, sigmoidoscopy, microsurgery, neurosurgery, colposcopy, ophthalmology/corneal surgery with microscope, ophthalmology/vitreous surgery with microscope, and ophthalmology/indirect examination and general surgery. In typical applications, the forward end of an endoscope is placed in the body cavity where viewing is desired. An illumination means is provided either as part of the endoscope or by a separate means. The endoscope end senses imagery in the cavity and transmits that imagery, typically by means of a fiber optic bundle to an output means at the end of the endoscope outside the body. The light signals delivered at the output end of the endoscope are then employed in a variety of ways, such as by direct viewing or through beam splitting by both direct viewing and to a camera for television viewing or by television viewing alone. Where it is desired to televise the endoscopy, the features desired in the camera are complex due to the large performance differences in different types of endoscopes, the reduced light transmission of endoscopes with age, the wide variety of light sources, the variation of type of cavity into which the endoscope may be inserted, and the need for ease of handling and light weight to facilitate use. Light transmission is a key variable among endoscopes. The type and size of endoscope greatly affects the amount of light transmitted from a subject to the television camera. For example, larger glass fiber bundles yield more light, hence, a brighter image which is easier to televise. The outside diameter of endoscopes of the same type may be an indication of the size of the glass fiber bundle. In general, shorter and larger diameter endoscopes transfer more light than longer or smaller diameter instruments. Operating endoscopes usually have smaller light transmission bundles than diagnostic types to permit channels for instruments, air, and/or water. Thus, it is usually easier to televise imagery from diagnostic endoscopes than from operating endoscopes, given the same medical circumstances.
Light transmission of fiber optic bundles in an endoscope declines with age. Also, usage tends to break individual fibers, reducing the amount of light transmitted. Exposure to heat gradually yellows the fibers, degrading light transmission and distorting the color. High usage endoscopes, therefore, requires brighter light sources or increased camera sensitivity for satisfactory television viewing. For maximum light transmission, an endoscope should have clean optics and light channels. It is important that the camera-light-source combination used in endoscopy provides sufficient sensitivity and intensity to produce a satisfactory color television image. Manufacturers of endoscopes offer several light sources having a great range of intensity. In selecting a light source, it is important to consider the viewing media in that television viewing requires a more brightly lit subject than direct ocular viewing. A common endoscopy problem is the dramatic reduction in image intensity resulting when the endoscope moves from a small body passage into a much larger cavity. In a small passage, there may be more than adequate illumination for a distance from the endoscope tip to the subject, for example, up to 20 millimeters. However, when the endoscope enters a larger cavity, the subject distance may increase, for example, up to 100 millimeters or greater. At 100 millimeters, the light on the subject is reduced by the inverse square of the subject distance to about 4 percent of the light available at 20 millimeters. In addition, the relative angle of the tissue to be viewed may change, altering the reflectivity of the surface. Further, small diameter cavities often act as a reflector directing light forward toward the viewing area.
Typically, for viewing video endoscopy, a 12-inch television monitor is satisfactory. The size of the image on a particular monitor is determined by the magnification of the endoscope. Image size as a percentage of screen height is important from the standpoint of brightness and resolution. As the image is enlarged to full screen height, the image resolution will increase because more video scanning lines are utilized. However, image brightness decreases as a function of the square of image size. With constant illumination and no light change, a 40 percent larger image will be 50 percent less bright.
A number of video cameras for endoscopy have been available. For example, a color television endoscope camera is made by Circon Corporation, Model MV 9330/35. This camera weighs 6 ounces and employs a pick up tube two-thirds of an inch in length. Also, Circon Corporation has had available various optical accessories, including couplers, eye piece adapters, and beam splitters. The resulting video system is sufficiently small and light that it can be mounted directly on any rigid or flexible endoscope. Since the color television camera receives a direct image from the endoscope, its image brightness, color fidelity, and resolution are superior to larger size cameras, which must be connected to an endoscope through articulated lenses or fiber optic links. Moreover, such links can cause image rotation and waste valuable image intensity, thereby interfering with the endoscopy process. For the interface of a video camera to an endoscope, an optical coupler is normally employed. The coupler connects the camera directly to the endoscope. Thus, all the available light goes directly into the camera, permitting the brightest possible television image. However, it is also possible to interpose a beam splitter between the endoscope and the camera optics for direct viewing as well as video monitor viewing. Furthermore, it is common to apply an adapter ring to the endoscope for easily removing the video camera or the beam splitter when used, thus providing direct viewing to the endoscope.
All video cameras compensate for some range of light level. However, that range is frequently exceeded when viewing tissue at varying distances from the distal tip of the endoscope and varies as a function cavity size. The result is washed out or darkened images. It can be seen that size, weight, and sensitivity are important features of video cameras for use in conjunction with endoscopes. The aforementioned Circon Corporation Model MV 9330/035 camera, for example, is 11/2 inches in diameter by 51/2 inches long and weighs six ounces. Another camera, also made by Circon Corporation, is Model MV 9320/25, which has particularly low light level sensivity, being about 10 times more light sensitive than any other color television endoscope camera. This camera is 11/2 inches in diameter by 51/2 inches long and weighs also six ounces. Its unique light sensitivity is particularly advantageous in televising very difficult microsurgery. The above-described devices are employed first by use of an adapter fixed to the end of the endoscope which receives an optical coupler having therein an optical system for passing the image to the camera. At the end of the coupler, a camera is attached. The coupler-and-camera combination receives optical imagery from the output end of the endoscope and converts it to preprocessed color video signals which are then transmitted for processing and projection on a color television monitor.
Although a high degree of miniaturization has been made possible by advances in the manufacture of electronic components and circuitry, and substantial light weight has been made possible similarly by advances in materials sciences, it is, nevertheless, very desirable to further reduce the size and weight of the entire endoscope video system, particularly that portion of the system which is directly attached to the end of the endoscope and which must be handled by medical personnel.